Abstract
Changes in butterfly populations are routinely monitored using transect counts, for example from the UK Butterfly Monitoring Scheme. However, abundance trends are typically only calculated at national and country level in the UK. A new method is presented that estimates species’ trends for smaller regions or datasets, where there may be limited transects. National approaches rely on larger numbers of transects and estimate flight periods either at site level, at the cost of excluding data, or assume a fixed flight period across transects to maximise data usage. The new approach uses butterfly records from all available sources to estimate a parameterised curve representing the flight period and create a so-called Dummy site. Counts from the Dummy site are included with true transect counts in a generalised additive model to estimate annual flight periods as fixed across sites, from which counts and abundance indices are estimated. Inclusion of the Dummy site produces a better overall fit, with greater influence for species with limited transects. Regional indices were often comparable with those produced from a national analysis, but with more realistic indices for some species. Trends were usually similar in magnitude and sign, but for certain species the new approach estimated more robust trends, benefiting from the inclusion of more data through estimating a common regional flight period. The approach is demonstrated for butterflies in Surrey (UK) but has wider relevance, for example to newly-established or small-scale monitoring schemes which may exploit alternative data sources to inform species’ flight period estimation.
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06 August 2020
In the Original publication of the article, Table 1 was published incorrectly. The correct Table 1 is given in this Correction.
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Acknowledgements
Many thanks to Ian Middlebrook for supplying the site indices from the national analysis, to David Roy for comments on an earlier draft of this paper and to the two anonymous reviewers who provided constructive comments of an earlier draft of the paper. The UK Butterfly Monitoring Scheme is organized and funded by Butterfly Conservation, the UK Centre for Ecology & Hydrology, British Trust for Ornithology, and the Joint Nature Conservation Committee. The UKBMS is indebted to all volunteers who contribute data to the scheme. With thanks to all recorders who contribute to the Butterflies for the New Millennium, which is run by Butterfly Conservation with support from Natural England.
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Harry E Clarke is the Surrey County Butterfly Recorder and a Butterfly Conservation volunteer
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Clarke, H.E., Dennis, E.B. A new method for calculating butterfly abundance trends for small regional areas. J Insect Conserv 24, 779–790 (2020). https://doi.org/10.1007/s10841-020-00251-1
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DOI: https://doi.org/10.1007/s10841-020-00251-1